1. Field of the Invention
This invention relates to an automatic guided vehicle for conveying, for example, parts and products on the way of manufacturing on the production line in a factory, or storing into or shipping from an automatic warehouse products or half-finished products on the way of manufacturing, and more particularly to an automatic guided vehicle which is adapted to keep a loading table provided thereon not-changed in the relative direction to a floor even when the vehicle is whirled to enter an assorting line or the like branched perpendicularly to a main travelling way.
2. Description of the Prior Art
Recently, the so-called factory automation has been progressed so that the automatic guided vehicle is often used to convey an object to be conveyed, such as a part, half-finished products, or products, in the factory, in the warehouse attached thereto, or between both.
FIG. 1-(a) is a schematic plan view of such automatic guide system, in which an automatic guided vehicle 4 in use, when moving forwardly in the direction of the unshaded arrow as shown n FIG. 1-(a) is usually provided at the upper portion with roller conveyor 4a which is capable of conveying the object 5 perpendicularly to the forward direction, in other words, sidewise of a main travelling way 1.
While, a station 30 where the object 5 to be conveyed is loaded on the automatic guided vehicle 4 or unloaded therefrom, for the so-called loading-unloading operation, is located on a point A halfway and sidewise of the main travelling way 1. Hence, the object 5 is unloaded to the station 30 from the automatic guided vehicle 4 or loaded to the automatic guided vehicle 4 from the station 30 by driving the roller conveyor 4a when the automatic guided vehicle 4 stops at the point A of the main travelling way 1.
The main travelling way 1 and many other stations, however, may not have the relation therebetween such that the station is located sidewise of the travelling way as at the point A showing in FIG. 1-(a), in other words, perpendicular to the forward direction of the automatic guided vehicle 4, but sometimes may have the relation in tha the automatic guided vehicle 4 is positioned at a point C with respect to the station 31 as shown in FIG. 1-(b), because of various conditions of route setting. In detail, the station 31 is located on the extension of the end of a branch 2 extending perpendicularly from the straight main travelling way 1.
In this case, operation as shown in FIG. 1-(b) is required to unload the object 5 from the automatic guided vehicle 4 to the station 31. In detail, the automatic guided vehicle 4 at first is moved forwardly on the main travelling way 1 from the point A toward a branch point B to the branch 2. Next, the vehicle 4 is whirled clockwise at an angle of 90.degree. and then enters the branch 2 to move toward a point C just before the station 31 which is located at the end of the extension of branch 2. While, the conveying direction of the object 5 by the roller conveyor 4a orients transversely of the branch 2, that is, perpendicularly to the extension thereof. Therefore, it is impossible to transfer the object 5 to the station 31. Hence, it is necessary for unloading the object 5 onto the station 31 to orient the roller conveyor 4a loading the object 5 toward the station 31, concretely, to whirl the body of the automatic guided vehicle 4 at an angle of 90.degree. just before the station 31.
In order to solve such problem, for example, the following construction is proposed to the automatic guided vehicle 4. In other words, driving wheels for travelling the automatic guided vehicle 4 are made turnable at an angle of 90.degree. (where driven wheels employ casters or the like) so that the automatic guided vehicle 4 is provided with function to travel transversely, that is, perpendicularly to the normal forward direction. The automatic guided vehicle 4 having such function, when it travels from the point A to that B on the main travelling way 1 as shown in FIG. 1-(c), turns the driving wheels each at an angle of 90.degree. with respect to the previous forward direction, in other words, in parallel to the branch 2 and then travels thereon. Hence, the conveying direction of the conveyor 4a coincides with the direction toward the station 31, thereby enabling the object 5 to be transferred from the automatic guided vehicle 4 to the station 31.
The conventional automatic guided vehicle, which is desired to be simple in construction, does not adopt a steering mechanism for changing each driving wheel in its direction, but allows a pair of right and left driving wheels to be rotationally driven independently of each other, thereby turning through different rotational speed of each driving wheel, or allows the driving wheels to rotate reversely to each other and at the same speeds, thereby changing the forward direction of the vehicle at one place. Hence, it is necessary for making the automatic guided vehicle travelable transversely as above-mentioned to construct the plurality of driving wheels each to be changeable of its direction. Accordingly, each driving wheel requires its steering mechanism in comparison with the conventional construction, thereby occurring problems in that control means for the steering mechanism is required and the automatic guided vehicle is complicated in construction.